The invention relates to a decorative panel composed of a core layer and a layer decorated on one or both sides and to a process for its production. Panels of this type are employed for interior or exterior uses in the building industry, being used as cladding panels or self-supporting units, depending on their thickness.
The decorative panels used hitherto are, for example, high pressure decorative laminates (H.P.D.L.) (DIN 19,926), as they are called. They are composed of a stack of paper webs impregnated with resin and compressed under hot conditions, as the core layer, and of a top layer made of resin-impregnated decorative paper. These panels have the disadvantage that they are attacked by mineral acids, especially at concentrations above 10% and at an exposure time longer than 10 minutes. In addition, in the standard embodiment, these panels are not adequately resistant to weathering, since the type of resin used in the top layer is sensitive to hydrolysis. Panels of this type can, therefore, only be used to a limited extent as work benches in chemical laboratories or for the production of wet cells which have to be cleaned with acids. If they are used for exterior purposes, additional expensive measures are necessary to improve their resistance to the effects of weathering.
Laminates and panels based on plastics, such as polyester or acrylate panels, are, however, particularly sensitive to scratching and are not adequately resistant to organic solvents. For this reason they are also not very suitable for these applications.
European application No. 85,105,851.1, which does not constitute a prior publication, relates to a decorative panel which is particularly suitable for exterior uses, for interior construction and for the production of special furniture, and which has a surface which is not sensitive to hydrolysis and is adequately resistant to the effects of weathering, mineral acids and organic solvents, and which also has a high surface hardness. This is composed of a core layer and a decorative layer on one or both sides. At least the outermost layer of the panel on at least one of the two panel surfaces is composed predominantly of a synthetic resin formed from one or more components, polymerized by radiation and selected from the group comprising unsaturated acrylates and methacrylates. This layer has a particularly high surface hardness. It is still scratch-resistant at a scratch loading of at least 1.5N, preferably 2 to 7N (DIN 53,799, part 10). In the process for the production of this panel, a liquid surface layer comprising the components which can be polymerized by radiation is applied to a substrate and is subsequently polymerized by radiation. The panel surface does not have the desired properties until after a further stage in which the surface layer which has been polymerized by radiation is compressed together with the substrate at an elevated temperature.
However, this decorative panel has the property, which is frequently undesirable, of exhibiting a certain degree of gloss. If texturized separating media are used in the final compression under heat, it is admittedly possible to give the panel surface a surface structure which is texturized in conformity with the surface of the separating medium, for example a surface structure similar to orange peel, but its surface gloss is, as before, very high. The addition of known delustering agents, such as silicon dioxide pigments, to the outermost surface layer of the panel also does not, for practical purposes, reduce the gloss, since the pigment-containing surface, which is initially still satin-frosted after the radiation polymerization, unaccountably becomes glossy again as soon as the panel is subsequently subjected to compression under heat.